My 243 AI does not seem to be shooting as well as it did. The barrel is newish with less than 400 softish rounds through it.
I neck turned a box of new Lapua 243 for fireforming (.268 loaded) using a Redding .266 bushing. I have now shot my way through the 100 and the second fireings are not as good as the first.. Checking the OD when loaded, all is well at between .2675 and .268 Scratching my head, I then had a look at the ID of the necks and these varey from .236 to .241 Obviously my neck tension is varied. Would this give me a problem and why has this happened with a uniform neck turning method.

Hello Johnny,

1) Could the problem be bullet seating depth?

2) Is bullet weight correct for rifle twist?

3) What is neck thickness before neck turning?

4) Do you weight sort your brass? This will help keep neck thickness in uniform groups.

5) The brass has a neck thickness tolerance. When the brass is run over a sizing mandrel before neck turning the neck thickness distortions are pushed to the outside and trimmed during the outside neck turning operation.

Recommendation: Try weight sorting your brass and shooting by weight groups and using a .264" Sizing bushing.

the inside dia means nothing. The necks after turning have different amounts of "spring-back" in them. If you CORRECTLY measured the neck thickness with a neck wall mic, then the inside dia measurement never comes into play as the neck thickness is concentric. Size them and then check inside dia,..it will be consistent. HTH

is this the first reload after fire forming?
What is the wall thickness of the round after turning?
did you trim to length?
do you have a tight neck chamber or is it standard?
.2675 to .268 bullet diameter is .243 + if the wall is .012x2 = .267
your bullet tension is -0- to .0005
I like to have my tension at .002
I also anneil after fire forming before neck sizing.
I have been using a lee collet die for neck sizing and found it to be more consistent than the redding neck dies i have.
were the fire formed cases fired using the same load?
The volume in the case has changed and you may need to go up in order to maintain the same pressure.
hope this sheds some light on your problem.
Dave

Neck turning means a couple of different things. Unless you have a tight chamber with exact dimensions given to you by the gunsmith, neck turning means "cleaning up" the neck ie. uniforming it to remove high spots. When you do this (gradually) you will see some place when brass was removed and others where it was not removed. This is as it should be. If you removed brass from the whole neck, and you do not have a tight chamber, then you almost certainly have brass that, when loaded, has a greater "gap" between the neck and the chamber. In addition, you may find that your sizing die does not have enough grip on the bullet. Why did you neck turn in the first place?
Peter.

hivelosity,

Why do you anneal before neck sizing rather than after neck sizing?

Thanks.

anneil before sizing.
I have found with the lee collet dies that the bullet pull was more consistent ( bullet grip) than if I did not anneil. I use a force guage.
on my long range 1000yrd, groups shrank from 15 to 20 inches down to around 8 inches. that was a big improvement for me.
now I anneil the necks after each firing.
also on the lee die i double stroke the press turning the case helps keep them streight.
Dave

Thanks Dave. That is a tremendous group improvement.

Thanks all.

The rifle is a .270 neck. At present using a Forster die to initially size the brass. Then using a Sinclair neck turning tool.
I have set it by turning to estimated amount. Load a bullet and see how far much more I need to turn. I then do this until I have a .268 when loaded with a Berger 68 or Nosler 70. I use a Redding Neck sizer with a .266 bushing.

The brass is on it's 1st fireing as AI formed. It was while sizing with the neck bushing that I found the ODs were consistant at about .267 but the ID difference was between .236 & .241
I must admit I have not checked the wall thickness on these.
What I will do is get 5 new pieced of brass and take measurements of ID/OD and wall thickness whilst turning.

I should have stuck with the standard Weatherby MKV in 243.....Far less hassle...

Johnny Foreigner,

It is just possible that when turning the brass that the cases were not lubed the same, or allowed to heat on the mandral. This will cause uneven neck thicknesses. (Yes, ask me how I know... ) The good news is theat the thicker ones can be made to match the thinner ones. Also if there is a significant degree of jump before the bullet enters the engraving stage or rifling inconsistant pull will show up on your targets. I have found the .243 AI to be a tempermental cartridge to load for, but rewarding when it delievers the goods. Stick with it, and vary the powder types, same me a lot of time!

Johnny, dont give up just get after it. we reloaders can get by that tiny little hump in the road.
I am not convinced that your measuring of the ID is accurate. its pretty hard to measure a round hole correctly with out a plug guage.
If you will explore a little you will find that ID may have a slight tapper to it and the reason is you turn the necks. at the sholder neck junction of the ID you will find a donut, that donut may move a few thousands up and down the neck depending on how much material was removed and how close you came to the sholder. Its hard to spot but once you discover it then you may see why you have so much variation on the ID.
Make a guage out of a paper clip. on one end bend the clip at a 90 degree angle to form an off center (T) from the rounded side to the end should measure .244 some adjustment may be needed for your cases, slowly slid the clip down the neck and where the donut is you will feel it as a hump. I use a Starrett plug guage It looks like a golf tee and is adjustable.

I believe that your problem is that Sinclair neck turner cutter. All these cutters I've examined are angled and cut only at the point . I attempted to use one once to turn a few cases -the result was a threaded case neck ! The tool would bite and screw itself onto the case neck -I guess it is suposed to cut on the return pass . If these cases are reloaded a few times the necks will be a different thickness as the ridges smooth out.
You could modify that cutter or have it surface ground by a local machine shop .

Try using a Hart NT : http://www.rwhart.com/ The carbide cutter cuts smoothly and very consistent necks are the result. It's Hart -nuff said!
The Forster NT is also an excellent tool a bit less expensive. The people there are great to deal with-the NT just keeps getting better with modified pilots and cutter finish- angles. http://www.forsterproducts.com/
The Jaco neck turner is a Ferris Pindel design still avaialable from A.J. Walker . I have one -do a search on Benchrest.com for pictures .
A ball mike to .0001 is really necessary to set up your tools and to check all the necks after your finished.
FP-10 works well as a neck turning lubrication.Imperial wax from Redding is fine also.
The 70 gr Nosler Bt has a parallel bearing surface at one diameter . They shoot very well in my 6 PPC.
The 65 -68 Berger has a slight pressure ring at the base -measure your clearance here .

Case necks as received can have a slight taper. When you size the case before neck turning it's possible to have the case mouth tight on the mandrel and base of the neck with a little clearance from the brass spring back.
So far I turn by hand as I feel this provides a more uniform case neck.
It would help to know exactly what you are doing to analyse this .
Glenn

You did run them through a FL die first to uniform the necks ?